Coating compositions formulated to include one or more material to provide anticorrosion properties, used for forming a film layer on the surface of metallic substrates, are known in the art. Such coating compositions make use of materials known to provide some degree of protection against corrosion by one of three different mechanisms.
A first mechanism of corrosion control in coating compositions is one provided by a formulation where a binder composition, that imparts a high degree of moisture and water diffusion resistance to the resulting cured film, is combined with a pigment or solid component that enhances the barrier properties of the film composition, thereby providing a physical barrier to any water passing into the cured coating film to protect the underlying coated metal substrate surface from corrosion. Further, this coating film has a high degree of adhesion to the metallic substrate, primarily through the adhesion properties of the binder component of the composition. Pigment materials or solid components useful in facilitating the barrier properties of the composition comprising the film include aluminum, iron oxide, mica, talc, talc, calcium silicate, and barium sulfate in particle and/or flake form.
A second mechanism of corrosion control in coating compositions is one provided by the placement of a desired material adjacent the metallic substrate surface that is selected to sacrificially corrode upon contact with any water and oxygen passing into the cured coating film, thereby sacrificially corroding to cathodically protect and prevent the underlying metallic substrate from corroding. Zinc metal is an example material useful in this regard, and can be provided on the surface of the substrate as a constituent in a coating composition or can be provided separately therefrom.
A third mechanism of corrosion control is one where the coating composition makes use of a material that is corrosion inhibiting, e.g., a corrosion inhibiting pigment, in that such material, upon being contacted with water, releases a material that diffuses to the substrate surface and either adsorbs on the substrate to form an impermeable layer which interferes with the corrosion reaction, or forms a reaction product with the surface of the metallic substrate or with the oxide layer on the surface, thereby preventing the surface from reacting with water, oxygen, and other corrosive materials. This operates to passivate the substrate surface and thereby protect it from corrosion. Materials known to be useful in this regard include calcium zinc phosphomolybdate, aluminum triphosphate, zinc phosphate, zinc iron phosphate, strontium zinc phosphosilicate, calcium phosphosilicate, zinc aluminum phosphate, lead-containing materials, and chromate-containing materials.
While anticorrosion coating compositions known in the art provide some degree of protection against unwanted corrosion, such coating compositions may rely on the use of materials that present a danger/hazard to the environment and/or a health or safety hazard to people and for these reasons the use of such coating compositions have or are being restricted or prohibited altogether. Additionally, such known coating compositions, while providing some degree of corrosion protection, are unable to provide a desired or needed level of corrosion control that is sufficient to meet the demands of certain end-use applications. The shortcomings of such known coating compositions can be caused by a failure of the particular corrosion control mechanism to operate effectively under actual exposure conditions and/or a failure/breakdown in the film itself formed from the composition.
It is, therefore, desired that an anticorrosion coating composition be formulated in a manner that provides a desired degree of corrosion control/resistance without the use of materials being regulated or otherwise known to present a hazard/danger to the environment and/or health or safety issues to people. It is desired that such anticorrosion coating compositions be formulated in a manner that provides a desired improved degree of corrosion resistance and film performance properties when compared to known coating compositions, thereby meeting the needs of certain end-use applications. It is further desired that such anticorrosion coating composition be formulated from readily available materials, and/or be made according to a process, that facilitates manufacturing the coating composition in a manner that does not require the use of exotic equipment, that is not unduly labor intensive, and that is economically feasible.